Recently, physical-layer network coding (PNC), a novel digital communication system, has aroused extensive interest of researchers. Similar to most other digital communication systems, the symbol timing plays an indispensable role in PNC. The existing research results, however, usually assume the symbol timing is fully known and rarely discuss the problem of symbol synchronization for PNC. In this paper, in view of the present situation, according to the maximum-likelihood estimation criterion we propose a new algorithm with a low oversampling factor (samples per symbol) based on the orthogonal training sequences. The proposed algorithm has the double advantage of a low sampling rate and high precision. It is shown by simulations that with a same oversampling factor, the proposed algorithm offers up to a 10-fold increase in the mean square error (MSE) performance over the conventional optimum sample (OS) algorithm for signal-noise ratio (SNR) of 5 dB.